今天在學習使用Spring Data JPA的時候，將bean和JpaRepository放在了不同的package中，導致無法構建項目，報以下錯誤：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'requestMappingHandlerAdapter' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter]: Factory method 'requestMappingHandlerAdapter' threw exception; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mvcConversionService' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.format.support.FormattingConversionService]: Factory method 'mvcConversionService' threw exception; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'readingListRepository': Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: Not a managed type: class bean.Book

異常是逐層拋出的，所以要定位到錯誤的地方，應該看最底下的內容，

java.lang.IllegalArgumentException: Not a managed type: class bean.Book

也就是我們沒有按照SpringBoot的約定,默認掃描(application.java 入口類相對的兄弟包及其子包)
解決方法1：將bean和JpaRepository放在同一個package中。
解決方法2：在JpaRepository上添加注釋，使得它能找到bean

@EntityScan("bean.Book")

這里整合以下常見的配置

@ComponentScan(basePackages = "com.boot.demo.xxx.*.*") 用于掃描@Controller @Service@EnableJpaRepositories(basePackages = "com.boot.demo.xxx.*.dao")? 用于掃描Dao @Repository@EntityScan("com.boot.demo.xxx.*.*") 用于掃描JPA實體類 @Entity

好吧，現在完全不知道spring-boot的文件結構要如何，多創建了幾個包，現在各種找不到類，controller也無法配置，明天繼續吧。

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